Optical conductivity of bismuth-based topological insulators

Abstract

The optical conductivity σ1(ω) and the spectral weight SW of four topological insulators with increasing chemical compensation (Bi2Se3,Bi2Se2Te,Bi 2-xCaxSe3, and Bi2Te2Se) have been measured from 5 to 300 K and from subterahertz to visible frequencies. The effect of compensation is clearly observed in the infrared spectra through the suppression of an extrinsic Drude term and the appearance of strong absorption peaks that we assign to electronic transitions among localized states. From the far-infrared spectral weight SW of the most compensated sample (Bi2Te2Se), one can estimate a density of charge carriers on the order of 1017/cm3 in good agreement with transport data. Those results demonstrate that the low-energy electrodynamics in single crystals of topological insulators, even at the highest degree of compensation presently achieved, is still influenced by three-dimensional charge excitations. © 2012 American Physical Society

Bulk Fermi surface and electronic properties of Cu0.07Bi2Se3

“…5 the remaining optical conductivity ∆σ 1 (ω) obtained after subtracting the Drude and the sharp phonon contributions. The data are similar to a very recent study on several Bi-based TIs [14], and we describe it the same way, in terms of two absorption bands: a low frequency FIR1, centered around 150 cm −1 , and a higher frequency one, FIR2 (≈ 400 cm −1 ). As was pointed out in Ref.…”

“…As was pointed out in Ref. [14], they resemble the phosphorous (P) doped silicon (Si), where P impurities give rise to bound states, with the outer electrons in a hydrogenlike potential [17]. The low frequency band, FIR1 in our case, would then correspond to hydrogen-like 1s → np transitions and the higher frequency (FIR2) to impurity ionization, i.e.…”

“…What is striking in our Cu doped sample (Fig. 5(b)) is that the amplitude of the FIR2 peak is several times larger than that observed in any of the previous Bi-based TIs [14], reflecting a large concentration of bound electrons. From energy considerations, it is expected that the bound states are created by Cu atoms that enter interstitially, within the Bi-Se ionic bond, or even by Cu atoms substituting for Bi in the crystal structure.…”

“…We also notice that the strong phonon mode near 60 cm −1 is almost completely suppressed with Cu addition, whereas the one near 130 cm −1 , barely observable in Bi 2 Se 3 at room temperature, appears enhanced in Cu 0.07 Bi 2 Se 3 . The vibrational modes in Bi-based topological insulators have been studied in detail elsewhere [13][14][15]; here, we restrict our discussion to the effect of Cu on the electronic structure. Figure 5(a) shows the real part of the optical conductivity σ 1 (ω) obtained after Kramers-Kronig transformation of R(ω) [16].…”

Optoelectronic devices, plasmonics, and photonics with topological insulators

“…37 Moreover, the amazing optical properties of TIs [38][39][40][41][42][43][44] allow their versatile and multifunctional use in signal emission, transmission, modulation, and detection.…”